Cut the butter into half-inch cubes and keep at room temperature until soft so that it can easily be mixed with a rubber spatula. The butter can also be softened by placing it in a microwave oven for thirty of forty seconds.
In a mixing bowl, cream the butter. Stir in the mustard, thyme and salt. Fold in the blue cheese and gently blend until all is incorporated. Taste for seasoning and add salt if desired.
With a rubber spatula, form the butter into two nine-inch logs along the bottom edge of two pieces of aluminum foil. The logs should be about an inch and a half in diameter. Roll each in the foil to the other end. Carefully twist the ends of the foil so that the butter forms into a tube. Continue to twist until just snug to complete the form. These can be kept in the freezer. If serving the same day, keep in the refrigerator at least four hours so the butter can harden for ease of serving.
From the logs cut one half-inch slice per portion of steak, hamburger, etc. Remove the foil then place on hot steaks and chops from the oven or grill.